We have all known colleagues who struggle into work when they are unwell, leaving a trail of germs that threaten the health of their co-workers – and then expect praise for their fortitude. Maybe you are one of them. So, should you do the decent thing and go home?

According to the Office for National Statistics, 141m working days were lost in 2018, with minor illnesses such as colds the most common reason for absence. Although the days lost to sickness have been falling since the early 00s, with a sharp dip since the 2008 recession, the reason is probably not that we are getting healthier, but that we are more worried about job security. Presenteeism has tripled to a record high since 2010, according to a survey by the Chartered Institute of Personnel and Development in 2018.

Still, it can be hard to know when you should stay at home and when it is OK to go to work. “A lot of it depends on what kind of job you do,” says Amir Khan, a GP. “If you’re working with people who are at risk, or with children or in healthcare, you should stay at home.”

With vomiting and diarrhoea – the norovirus winter vomiting bug, for example – it is more clear cut. The bug is short-lived, but highly contagious, so you should stay at home for 48 hours after the last episode of vomiting and diarrhoea. However, the GP and writer Ann Robinson points out that some people can have persistent diarrhoea after a stomach bug. “It can take up to three weeks to go back to normal,” she says. “There’s no real reason to stay at home, as long as you’re not dehydrated. But you do have a social responsibility to wash your hands properly after going to the toilet.”

It is less easy to know when to stay at home with a cold. Robinson thinks that if you are well enough to get up and about, you are probably well enough to go into work, while taking precautions to try to avoid spreading it.

“You should stay at home if you have an illness that involves a fever, because that usually means it’s still in its contagious form,” says Khan. “If you’re sneezing and coughing, you are spreading disease, but you will have had it for a couple of days before you knew about it, and that’s when it’s at its most contagious. These diseases are designed to spread.”

A cold can be contagious for several days after symptoms appear, and even up to two weeks – but it would be unrealistic to expect to take two weeks off work for a cold. If you catch flu, expect to be infectious for up to a week. According to the NHS, you are most likely to give it to someone in the first five days.

If you are ill, there are measures you can take to try to prevent your germs spreading too liberally. There are also things you can do to avoid picking up infections.

“Your risk of catching something will be directly proportional to the proximity to the ill person,” says Robinson. “If they insist on throwing used tissues in a bin near you, I would move away, or make it clear that it’s a highly antisocial thing to do. Keep your distance. Don’t share cups.”

You should also wash your hands regularly, particularly before eating.

Nasal sprays are marketed as a way to prevent getting a cold, but Robinson is sceptical. “There is a rational basis for spraying a saline solution – nothing more expensive than saltwater spray – up your nose at night, because it’s true that this is the way the virus enters your system. I’m not aware of any good evidence, but it makes a little bit of sense. What you’re really doing when you spray saline up your nose is perking up the cilia, the little hairs in your nose, which are an important line of defence. You’re not actually ‘washing out’ a virus.”

Instead, work on supporting your immune system. Get enough sleep, manage stress and take regular exercise. “Have a healthy diet with lots of green vegetables,” says Khan. “Even though there isn’t much of it at the moment, sunlight is brilliant for the immune system, so, if you can, get outdoors and get some sun.”

Khan comes into contact with lots of coughing and sneezing people in his surgery. “I am so cautious,” he says about his own health. He recommends carrying a bottle of hand-sanitiser gel. “It won’t kill the norovirus, but it will kill the common cold and cough viruses.”

What if someone around you is spluttering? “Use the gel on your hands because, chances are, they’ve touched something you’re about to touch,” he advises. “Put some gel on a tissue and wipe down any surfaces that other people may be using, such as your workstation.”

He also recommends wiping door handles and chairs regularly. Cold viruses can live for up to a week on hard surfaces, such as desks or kitchen worktops, and flu viruses can survive for about 24 hours.

But you can’t eliminate the risk – and if you do come down with a bad cold, you may not have picked it up from the person sneezing at the desk next to you. “You will have been exposed to things on your daily commute into work or in a coffee shop, so it’s not really fair to socially ostracise an individual,” says Robinson. “You’re exposed to viruses all the time.”